This invention relates to automatic control valves utilized in process control in a variety of industries. All such valves operate on the principle of converting potential energy (upstream pressure) into kinetic energy (fluid velocity) which then, depending on the desired downstream pressure, converts kinetic energy into turbulence which magnitude corresponds to the pressure differential across the valve. This process, while effective, is relatively inefficient since it reduces available potential energy downstream of the valve.
Newer valve types (see FIG. 4) try to reduce such energy loss by utilizing venturi type contours downstream of the valves throttling orifice. Here the process is as follows: When sufficient outlet pressure is reduced, the velocity within the throttling orifice reaches sonic velocity, when gaseous fluids are used. The gas now gradually expands within the venturi section until the desired downstream pressure is reached, thus avoiding most of the energy lost due to turbulence. This process is called isentropic recompression. The amount of avoided turbulence depends on how streamlined the fluid path is from the inlet port to the outlet of the valve. This requires that the cross-sectional flow areas have to evenly decrease towards the throttling area and gradually expand thereafter, thus avoiding sudden velocity changes. The prior art, exhibited in FIG. 4, does not fully meet such requirements due to the highly curved inlet section of the valve housing.
In contrast, this invention, being an inline version, avoids this problem and fulfills all of the above requirements. The invention thus is capable of recovering nearly ninety percent of the inlet pressure in contrast to a typical conventional control valve which is able to recover barely thirty-five percent under identical flow conditions, as exemplified in curves (a) and (b) in the attached FIG. 5.
A typical application for this invention, herein called a high recovery valve, is in a fuel control for gas turbines. Here the pressure recovery translates into available calories or heat content of the gas. More available calories downstream of the flow control valve positively affect the turbine efficiency defined as the ratio between thermal energy input and mechanical power output.
Another prior art is exhibited in International Patent number WO 97/18419 showing a Fluid Control Device with Reduced Noise Generation. It shows an inline tubular device having a circular inlet section (24) followed by a curved inlet (62) to an orifice (63) and ending in a venturi shaped outlet (64). Here the fluid passes a large inlet area followed by a sharp acceleration towards the orifice and the gradually slowing down toward the outlet. Such a schema is very beneficial for high pressure reduction of gases normally exhibiting high noise levels which can exceed 100 decibels. The function of the orifice inlet is to produce sonic velocities of the gas. Gradually increasing areas such as shown in the invention are absent, while not required.
Whenever the pressure at the valve orifice recedes below 50 percent of the inlet pressure, the resultant velocity at and beyond the orifice can reach super-sonic speeds of up to Mach 2.6. The result is a pattern of shock waves converting the resulting kinetic energy into heat and a lower downstream pressure through a process called “non-isentropic recompression”. While sound power at jet velocities below Mach 1.4 increases to the 6th power of the velocity, the sound power only increases to the second power of the Mach number at higher velocities (Reference: Baumann, Hans D. “A Method for predicting Aerodynamic Valve Noise Based on Modified Free Jet Noise Theories”, ASME paper; 87-WA/NCA-7)).
In addition, higher velocities create higher sound peek frequencies which reduce pipe external sound by 6 dB for each doubling of the frequency due to higher transmission losses of the pipe wall. One can see from all of this, that it is advantageous for noise reduction to shift jet velocities into higher Mach numbers using venturi type outlets. The aim of this prior art device is opposite of that of the invention. In the invention, pressure losses are avoided at all cost, while the prior art device requires high pressure losses to function properly.
These and other features and advantages are more clearly shown in the following detail description and accompanying drawings.